Gypsum | Define Gypsum at Dictionary.com gypsum noun 1. a very common mineral, hydrated calcium sulfate, CaSO 4 ⋅2H 2 O, occurring in crystals and in masses, soft enough to be scratched by the fingernail: used to make plaster of Paris, as an ornamental material, as a fertilizer, etc. Origin of gypsum 1640-50; < Latin: chalk < Greek gýpsos chalk, gypsum Dictionary.com Unabridged Examples from the Web for gypsum Expand Contemporary Examples The sand dunes were relentlessly mined in the past century; power lines and a gypsum plant split the park. The Economic Aspect of Geology C. K. Leith These meadows are divided by chains formed of red clay, and huge masses of gypsum, with here and there a pyramid of gravel. Old Mackinaw W. P. Strickland. British Dictionary definitions for gypsum Expand noun 1. a colourless or white mineral sometimes tinted by impurities, found in beds as an evaporite. It is used in the manufacture of plaster of Paris, cement, paint, school chalk, glass, and fertilizer. Composition: hydrated calcium sulphate.

Formula: CaSO4.2H2O. Crystal structure: monoclinic Derived Forms C17: from Latin, from Greek gupsos chalk, plaster, cement, of Semitic origin Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012 Word Origin and History for gypsum Expand n. substance (hydrated calcium sulphate) used in making plaster, late 14c., from Latin gypsum, from Greek gypsos "chalk," according to Klein, perhaps of Semitic origin (cf. Arabic jibs, Hebrew gephes "plaster").

Online Etymology Dictionary, © 2010 Douglas Harper Amici di TP article Caption: Lalli-Persiani Palace-Building[1] A museum for chalk but also an entire village inside a museum: this is an old idea that has re-emerged recently (1996) to safeguard what is left of the most typical work traditions of Gessopalena[2], extraction and working of the chalk rock. The original nucleus of the village lies on a mass of this chalk rock. In the past few months, following excavation work, various buildings of the Old Village have been recovered. After the war, following the frightful collapse of the eastern wall of rock that lies above the old quarry, the "Pretalucente[3]" (Shining Stone[4]) was irredeemably disfigured. Although various premises belonging to the Town Hall are available to exhibit craft and agricultural tools and equipment, old photos and other things that visually represent the history of chalk workers, none of them has the typical characteristic structure of a "living" museum, rather than a "dead" one; not even some of the recently restructured buildings in the Old Village.

There is, however, a private building which has all the characteristics needed for a live museum, as old as the Old Village itself, of which today it represents the most interesting part, even if it is little known. This is the huge cellar of the Persiani Palace, whose owner, Aureliano Lalli Persiani, has said it is available for the Town Hall to make use of, provided they equip it as a museum. The manner and timing of its use are yet to be decided and verified. This is an opportunity that the Town Hall and the cultural associations of Gessopalena, as well as the citizens interested in the history and guardianship of their wild native village, cannot afford the luxury of allowing to pass them by. This opportunity will not arise again, and, with the demographic crisis that is taking place in our villages, (if we do not grasp it) this last possibility of fixing with dignity a part of our historic past and leaving it to the few descendants who will follow on, will disappear. The cellars of the Persiani Palace, which figure as the only almost intact bastion placed at the entrance of the Old Village, were dug out of the chalk.

Until the 1940ï¿½s and 1950ï¿½s they were the site of an olive-press, a stable ï¿½ which later became a garage ï¿½ and a normal warehouse for food products. Visiting the cellars one has the impression of entering and exiting a series of Chinese boxes, with steps, windows and French doors inserted and carved into the rock, like in olden times. It is a fascinating experience, but unfortunately it has been put in danger by recent repaving, undertaken by the Town Hall, of the overhanging little road, Via Castello, at the entrance to the village. This gives rise to continuous flooding of the Persiani cellars due to infiltration by rain water which drips off the chalk walls, endangering them in the long run, and also the structure of the Palace. The foundations of this building rest on the underlying rock walls. Another problem is that the restructuring and support works carried out by the owner himself in the last few years, now risk being irredeemably worn out. Aureliano Lalli Persiani did not put up controversial posters, nor did he write to the newspapers, or use any other gaudy methods.

He simply let the problem be known, which arose a year ago when a local firm repaved about 20 metres of Via Castello. Renewing the water resistance (impermeability) of the little road would not be excessively costly, rather there would be a gain for the entire "chalk community" of Gessopalena, for they would then have full use and enjoyment of the cellars of Gessopalenaï¿½s oldest Palace (which in its present form dates back to the 17th Century). Its owners, the Persianis, have been protagonists in the history of the province of Chieti for several hundred years, but even this is something the "chalk" villagers of Gessopalena are ignoring. Translator's notes: [1] The Italian word "Palazzo" means both "Palace" and "Building". It is difficult in this case to know which of the two words it would be better to use, either could be appropriate, hence I have used both! [2] Gessopalena - This small mountain village in Abruzzo takes its name from the chalk quarries of the area, and has a wealth of medieval monuments. It lies to the right of the Aventine Valley.

Gessopalena dominates the surrounding countryside, including the "La Morgia" rock formation see:- Historically this domination was useful in its defence, and also the village could protect the way to the rich pastures of the Majella when necessary. Gessopalena was inhabited in prehistoric and Roman times; its written history dates from the 12th Century AD. In the early Middle Ages Gessopalena consisted of a group of houses clinging to a big rock called "Pietra Lucente" (Shining Stone) on top of which was an ancient castle. At that time Gessopalena was the main commercial centre in the Aventine valley. Later on the population moved downwards along the ancient "Via Peligna" to the site where the modern town is today. [3] "Pretalucente" (dialect) = "Pietra Lucente" or Shining Stone ï¿½ an old name given to the rock on which the ancient village of Gessopalena was built.

[4] Shining Stone ï¿½ The rock underneath Gessopalena is Gypsum (Hydrated Calcium Sulphate) used to make plaster of Paris, blackboard chalk, wall board, some cements, paint filler, ornamental stone, fertiliser etc. Since the mountainside on which the ancient village lay was a huge mass of gypsum, due to its particular crystalline structure, from some angles it can take on a certain shine and depending on how the rays of the sun would strike it, at certain times of day it would become especially brilliant and shining. Gypsum is one of the more common minerals in sedimentary environments. The largest deposits known occur in strata from the Permian age. It is a major rock forming mineral that produces massive beds, usually from precipitation out of highly saline waters. Since it forms easily from saline water, gypsum can have many inclusions of other minerals and even trapped bubbles of air and water. Gypsum has several variety names that are widely used in the mineral trade:- Selenite is the colourless and transparent variety that shows a pearl like lustre and has been described as having a moon like glow. The word selenite comes from the Greek for Moon and means moon rock.

Satin Spar is another variety; it has a compact fibrous aggregate. This variety has a very satin-like look that gives a play of light up and down the fibrous crystals. Alabaster is a fine grained massive material and is an ornamental stone that has been used in fine carvings for centuries, even eons. Desert Rose - Rosette shaped Gypsum with brown sand inclusions. Gypsum Rock - Rock composed mostly of the mineral Gypsum, but also contain impurities such as Calcite, Anhydrite, Rock Salt, Dolomite, Limonite, and clay. Gypsum is one of the most widely used minerals in the world and it literally surrounds us every day. Most gypsum in the United States is used to make wallboard for homes, offices, and commercial buildings; a typical new American home contains more than 7 metric tons of gypsum alone. Moreover, gypsum is used worldwide in concrete for highways, bridges, buildings, and many other structures that are part of our everyday life. Gypsum also is used extensively as a soil conditioner on large tracts of land in suburban areas, as well as in agricultural regions. Industrial uses Sheetrock or wallboard, a construction material Plaster. a construction material.

Solidifying earth (cast earth construction) Name Origin: Gypsum from the Greek, gyps meaning "burned" mineral. Selenite from the Greek in allusion to its pearly lustre (moon light) on cleavage fragments. The word gypsum is derived from the Greek meaning 'to cook', in reference to the burnt or calcined mineral. Because the gypsum from the quarries of the Montmartre district of Paris has long furnished burnt gypsum used for various purposes this material has been called plaster-of-Paris. In a small number of Gypsum specimens, water gets trapped inside a crystal in a hollow channel while the crystal forms. When such a crystal is rotated, a water "bubble" moves around inside it toward the lowest point in the channel. Such specimens are considered a mineralogical oddity, and are very much sought after by collectors. Gypsum is an industrially important mineral. It is the primary ingredient of plaster-of-Paris (finely ground Gypsum) and is also used in the production of cement. It is also the main component of sheet-rock. It is used as a flux for creating earthenware, and can be used as a fertilizer.

The variety Alabaster is carved for ornamental use, such as artistic sculptures and pottery. It is porous and is therefore easily dyed. The fibrous Satin Spar variety is sometimes cut into cabochons for collectors because of its strong cat's eye effect. Fine Gypsum specimens are very popular among mineral collectors, especially the varieties Selenite and Desert Rose. 4. Group of fragile acicular crystals 5. Platy rosette crystals 6. Long, slender, bent crystal 7. Satin Spar Heating gypsum above approximately 150ï¿½C (302ï¿½F) partially dehydrates the mineral, by driving off exactly 75% of the water contained in its chemical structure. The dehydration (specifically known as calcination) begins at approximately 80ï¿½C (176ï¿½F) and the heat energy delivered to the gypsum at this time (the heat of hydration) goes into driving off water (turning it into water vapor), not into increasing the temperature of the mineral. As water is lost, the temperature of the gypsum slowly increases until all the water has been removed, then begins rising normally at a quicker rate.

The ability of hydrated gypsum to remain at relatively low temperatures, even if a flame is applied directly to it for a short period of time, is exploited by drywall to confer fire resistance to the wooden frames of houses and other buildings. Even if a fire is impinging directly on a sheet of drywall, the wood frame behind it will remain at a relatively low temperature, preventing the destruction of the wood and the collapse of the structure, (until eventually too much water has been lost from the gypsum, when the wood will heat up and then burn). The partially dehydrated mineral is called calcium sulphate hemihydrate or calcined gypsum (though more commonly known as plaster of Paris). Calcined gypsum has an unusual property: when mixed with water at normal (ambient) temperatures, it recombines with the water that was driven off during calcination, and then sets to form a strong gypsum crystal lattice; this property is made use of in forming plaster casts to set broken bones. Most minerals, when rehydrated, simply form liquid or semi-liquid pastes, or remain powdery.

Gypsum, on the other hand, forms a strong crystal structure immediately upon receiving the water, and this phenomenon is responsible for gypsum's ease of being cast into sheets (for drywall), sticks (for blackboard chalk), molds (to set broken bones, or create molds for metal casting), and other forms. Small amounts of calcined gypsum are added to earth to create strong structures directly from cast earth, an alternative to adobe (which loses its strength when wet). Calcium carbonate Calcium carbonate Calcium carbonate Three types of calcium carbonate-containing rock are excavated and used by industry. They are limestone, chalk and dolomite. Limestone and chalk are both forms of calcium carbonate and dolomite is a mixture of calcium and magnesium carbonates. All have impurities such as clay but some rocks are over 97% pure. Limestone and other products derived from it are used extensively in the construction industry and to neutralise acidic compounds in a variety of contexts. In the chemical industry, large quantities of limestone are heated to ca 1500 K to form calcium oxide, known as quicklime: Water can be added to lime to form calcium hydroxide. The process is known as 'slaking'.

Solid calcium hydroxide is known as slaked lime or hydrated lime, and solutions and suspensions in water as milk of lime. The term lime is often used to cover quicklime, slaked lime (hydrated lime) and milk of lime. For a particular use, an appropriate choice is made from the four: limestone, quicklime, slaked lime or milk of lime. In many uses, lime reacts more quickly than limestone but is more expensive, because a high temperature is required to produce it from limestone. Uses of limestone and lime Figure 1 Principal uses of limestone and lime. The principal uses, by far, of limestone and lime are in the construction industry and cement making. They are also used in the chemical and metallurgical industries and in agriculture.

On a worldwide basis, the proportions of lime used in different industries are: 60% metallurgy (mainly steel manufacture , slag formation and its use in the blast furnace ) 25% construction (for example, it is used with asphalt in road paving, to stabilize soils and in making mortar and plaster) 15% for chemical and industrial uses (for example to make bleaches used in the manufacture of paper, to make precipitated calcium carbonate, a fine powder used in coatings for paper and paints, and in refining sugar to remove colloidal impurities) and for environmental uses (for example, with soda ash by both municipal authorities and industry, to soften water (remove calcium and magnesium ions), in the treatment of sewage to remove colloidal particles and in flue gas desulfurization ) However, these proportions vary widely from country to country.

For example, in the US, the proportions are: 38% metallurgy (mainly steel manufacture) 31% environmental uses (for example, with soda ash, by both municiipal authorities and industry to soften water (remove calcium and magnesium ions), in the treatment of sewage, to remove colloidal particles and in flue gas desulfurization 22% chemical and industrial uses (for example to make bleaches used in the manufacture of paper, to make precipitated calcium carbonate, a fine powder used in coatings for paper and paints and in refining sugar to remove colloidal impurities) 8% construction uses (for example, it is used with asphalt in road paving, to stabilize soils and in making mortar and plaster) 1% others Data from the US Geological Survey, 2012 The uses are described below, in more detail, in terms of different industries. In the construction industry Limestone has been used as a building material since the Stone Age. Indeed, the largest use of limestone and the various forms of lime is still in the construction industry, particularly in road building and building projects, from vast in size, bridges and skyscrapers, to houses.

Large lumps of calcium carbonate are often used where sizeable quantities of aggregate are needed, for example for the foundations of roads. Lime is often used to make soil firmer. It reacts with clay minerals in the soil to form cement-like compounds (for example calcium silicate and calcium aluminate (calcium aluminosilicate)), Figure 2. Figure 2(a) Clay particles are surrounded by water, allowing them to be aligned and able to slide easily. This results in a clay soil with a low strength. Figure 32b) When lime is added, the amount of water around the clay particles is reduced. The clay particles are no longer able to slide easily and the soil is strengthened. The strengthening of soil enables the construction of buildings by giving a more stable foundation. Lime is also used on building sites to allow large vehicles to move more easily (Figure 3). Figure 3 The wet soil has been made harder by the addition of lime. This earth-moving equipment is able to move around easily. By kind permission of Singleton Birch. Limestone is also the main constituent of cement and concrete.

In cement making Cement is made by heating a mixture of limestone and substances such as clays (which contain silica, alumina and iron(III) oxide) in kilns at high temperatures until it almost fuses. The mixture is then cooled and ground to a fine powder and mixed with calcium sulfate (gypsum). This is cement. It is essentially a mixture of calcium aluminosilicate and calcium sulfate. When it is mixed with water, chemical reactions occur to form a hard solid, impervious to water. About 3.6 billion tonnes of cement is produced annually, of which China accounts for 2.1 billion tonnes. Cement powder is usually mixed with sand and aggregate (gravel, granite) and when needed, they are mixed with water to form concrete. Figures 4 and 5 Builders and masons, prior to the use of modern cement, used a mixture of lime (calcium hydroxide), sand and water, known as lime mortar or simply mortar. It has been used for over 6000 years, since the buildings of Ancient Greece and Rome. When these buildings are renovated, lime mortar is used rather than cement.

In these photographs of York Minster, a relatively modern building dating back only 900 years, lime mortar has always been used in renovating the stonework that has to be replaced because of weathering over the centuries. By kind permission of Jessica Waddington. In industry and the environment Many lakes have become too acidic because of aerial pollution (acid rain), for example in the US, Scandinavia and Scotland. The lakes are sprayed with very finely powdered calcium carbonate (Figure 6). Another effective way to treat this problem is to apply the powdered limestone to unplanted areas near to the sources of the streams leading to the lakes. Figure 6 Powdered limestone is being sprayed over a lake near Hemsjö, in Southern Sweden. By kind permission of Rickard Gillberg. Limestone and the various forms of lime are used in large quantities to clean up the environment, by neutralising acids. For example, limestone and quicklime are used to remove sulfur dioxide produced in the burning of coal in power stations. Even 'clean' coal can contain about 1% sulfur. The gaseous effluents, flue gases, from the burning of the coal are passed through a spray of very finely ground limestone or quicklime suspended in water.

The sulfur dioxide, being an acid, reacts with them, for example: The resulting calcium sulfite collects at the base of the absorber and compressed air is blown into this residue. The calcium sulfite reacts with the air to form calcium sulfate (gypsum), used to make, for example, plaster board and cement. Very fine and pure calcium carbonate is used as filler in plastics and paper. A filler is a substance that gives bulk but does not alter the properties of the substance to which it is added and is also inert. Calcium carbonate when very finely crushed (less than 2 microns) is used in paints to give a 'matt' finish. Figure 7 Uses of limestone. Calcium carbonate is also used: to make sodium carbonate by the Solvay process in the blast furnace to make iron in the manufacture of glass The uses are further summarized in Figure 7. In agriculture Crushed limestone and lime in all its forms are used to neutralize acids in the soil and so create the optimum soil conditions for crop growth. They also help to break down clays as described above, improving the soil structure, thus improving drainage and reducing soil erosion. Further, they provide a source of calcium ions that are an important plant nutrient.

Annual production of limestone Data for the annual production of calcium carbonate are not readily available. Approximately 1 billion tonnes of its two principal ores, limestone and dolomite, are mined annually in the US. Given the relative amounts of lime that is used in different countries, an estimate of worldwide mining of calcium carbonate is 15 billion tonnes a year. Annual production of lime (calcium oxide and calcium hydroxide) World Data from the US Geological Survey, 2012 Manufacture of calcium oxide (quicklime) Calcium carbonate (limestone) is heated to form calcium oxide (quicklime) and carbon dioxide: It is an endothermic reaction and the equilibrium lies far to the left at low temperatures. Only at about 1200 K does the partial pressure of carbon dioxide exceed atmospheric pressure and the decomposition proceeds to completion. Quicklime is produced in refractory-lined kilns. Many designs are used, but the most common are based on the Vertical Shaft Kiln (Figure 8). The kiln is made of steel, lined with refractory bricks. The limestone is fed in from the top and air is either sucked by fans or pushed by roots type blowers, through the kiln from the bottom (counter flow).

The fuel is fed through the sides of the kiln, using about 8-10 lances inserted around the kiln. The lime kiln consists of three principle zones: in the preheating zone, the heat in the combustion products, including carbon dioxide from the dissociation of limestone, is used to preheat the limestone to 1200 K in the burning zone the limestone is decomposed to quicklime at gas temperatures of 1500 K, a process known as calcining in the cooling zone, the heat in the quicklime leaving the burning zone is used to preheat the air required for combustion to 600-750 K. The fuels used vary, depending on what is available. Many kilns use natural gas but in others oil is pumped in. In others, solids, such as finely powdered coal is pressurized and pumped in so that it acts as a fluid. If there is not enough air to complete combustion of the fuel, more is fed in directly to the burning zone. Figure 8 Manufacture of lime: The vertical shaft kiln. Many recently introduced kilns have two parallel units (Figure 9). They are known as two-shaft kilns.

In the simple single kiln, described above, the air is pumped up the kiln as the limestone flows down. This is known as a counter flow system. In the two-shaft kiln, known as the Parallel Flow Regenerative (PFR) lime kiln, the air and combustion gases travel parallel to the limestone. The fuel is injected just above the burning zone and the limestone absorbs most of the heat released by the fuel and so the temperature of the burning zone can be reduced to 1400 K, the temperature of the decomposition of limestone. Figure 9 Manufacture of lime: The Parallel Flow Regenerative (PFR) lime kiln. By kind permission of Maerz Ofenbau AG. Figure 10 A Parallel Flow Regenerative (PFR) lime kiln in Mexico. By kind permission of Maerz Ofenbau AG. In the diagram, the left-hand shaft is described as in burning mode. The exhaust gases cross over into the right-hand shaft, which is said to be in non-burning mode. These hot gases travel up in counterflow to the stone, heating it up ready for the right-hand shaft to become the burning shaft and the left-hand shaft becomes non-burning.

Each shaft cycles through the burning and non-burning mode about every 10 minutes. There is a large reduction in the fuel used by the two-shaft kiln compared to the single shaft kiln. Shaft kilns have capacities for producing up to 800 tonnes of lime per day. Quicklime is generally sold either as granules or as a finely ground powder. Manufacture of calcium hydroxide (hydrated lime) The reaction of quicklime with water is exothermic. Powdered calcium hydroxide is produced by hydrating quicklime with a controlled excess of water to make a dry product. Milk of lime is prepared by slaking quicklime with an excess of water. Date last amended: 28th November 2013 Minerals Minerals Minerals Minerals -Azurite: Azurite is a (hydrous copper carbonate) is found in elongated or tabular crystals. It also occurs as a film or granular mass. Azurite is semi-hard (3.5-4 on the Moh's Scale), heavy, fragile, with fairly good cleavage.

This beautiful blue mineral is associated with carbonate rocks, and is often found with malachite, calcite, chrysocolla and other secondary copper minerals. It is a valuable ornamental and collector's specimen, and most prized for display purposes. This particular specimen was found in the " Midelt" region of the Sahara desert in Morocco, where most of the world's greatest specimens come from. -Aragonite: The name Aragonite is derived from the location of Molina de Aragon, Spain. Aragonite occurs in Agrigento, Sicily, Italy, in the famous sulfur mines. It has also been found on Mount Vesuvius, Italy, at Monte Somma. It occurs with Siderite in Styria, Austria. Much Aragonite has come from various places in Cumbria and Cumberland, England. Giant masses were found in Ota City, Shimane Perfecture, Honshu, Japan. Interesting reddish crystal growths are abundant in Tazoula, near Sefrou, Morocco. Australia has also produced much material, in practically all its states. Aragonite formed from precipitating water that traps in organic matter, such as leaves, twigs, and moss.

Also calcareous mounds formed from deposition of hot springs that trap in organic matter. Aragonite can occur in many different colors ranging from Colorless, white, brown, gray, yellow, reddish, pink, purple, light blue, to light green. It has a hardness of 3½ - 4. Its composition consists of, Calcium carbonate, sometimes with some strontium, lead, and zinc. Its Chemical formula is: CaCO3 The most common crystallized form of Aragonite that we deal in is in ball-like protrusions of pseudohexagonal crystals. Which is found in Morocco. Aragonite is also said to contain metaphysical, and healing properties. We at Pangaea Industries do not endorse these claims, but we feel that it is our obligation to pass on the information. Aragonite: Deep, peaceful meditation; uplifts emotions. Centering, overview, patience under stress, helps navigate business/managerial/personal challenges with a clear head and steady hand. Giving and receiving easily. Balances yin-yang. Eyes, brain, Central, Nervous System, heart, opens spiritual/brow C for day-to-day living with an open heart and mind.

- Calcite: Calcite belongs to the calcite group, a group of related carbonates that are isomorphous with one another. They are similar in many physical properties, and may partially or fully replace one another, forming a partial solid solution series. All members of the calcite group crystallize in the trigonal subdivision of the hexagonal system (as rhombohedrons and scalenohedrons), have perfect rhombohedral cleavage, and exhibit a strong double refraction in transparent rhombohedrons. Calcite is the one of the most common minerals on earth. It occurs in a seemingly unlimited variety of shapes and colors. It constitutes a major portion of many of the earth's rocks. Calcite's chemical formula is,CaCO3 it has a hardness of 3, and it occurs in all colors, sometimes even multicolored. Its composition consists of, Calcium carbonate, commonly with some impurities of either iron, magnesium, manganese, and occasionally with zinc and cobalt. Among the rocks formed from Calcite are, Limestone, Marble, and Chalk. Calcite, like Aragonite formed from precipitating water that traps in organic matter, such as leaves, twigs, and moss.

Also calcareous mounds formed from deposition of hot springs that trap in organic matter. Our calcite specimens are in the form of geodes. The surrounding matix of the calcite crystals is chalk. They were found in the Atlas mountains in Morocco. -Vanadenite: Vanadinite is a mineral made up of lead vanadate and chloride. It is found in yellowish, brownish, or ruby red hexagonal crystals. Our vanadenite specimens were found in the "Midelt" region of the Atlas Mountains in Morocco, which is considered to be one of the richest mineral formations in the world. -Selenite: is a varietal name of Gypsum, which is one of the more common minerals in sedimentary environments. It's primarily composed of Hydrated Calcium Sulphate, it forms when limestone is attacked by sulphuric acid.The resulting product is larger than its components so can be 'squirted' through pores in the rock under pressure,whilst in crystalline form. It is a major rock forming mineral that produces massive beds, usually from precipitation out of highly saline waters. Since it forms easily from saline water, gypsum can have many inclusions of other minerals and even trapped bubbles of air and water.

Gypsum has several variety names that are widely used in the mineral trade. "Selenite" is the colorless and transparent variety that shows a pearl like luster and has been described as having a moon like glow. The word selenite comes from the greek for Moon and means moon rock. Another variety is a compact fiberous aggregate called "satin spar" . This variety has a very satin like look that gives a play of light up and down the fibrous crystals. A fine grained massive material is called "alabaster" and is an ornamental stone used in fine carvings for centuries, even eons. All prices are in USD. Copyright 2017 Pangaea Industries / FossilsPlus.com. Connect with us: MIA Technical Bulletin Onyx Tanzania Turkey In all stone species, quarries are completely unique, although this may be more true of onyx Quarries than any other dimension stone type.

Perhaps the most impressive onyx quarries, as far as mass is concerned, are those located in Baluchistan (Eastern Pakistan) where the depth of the onyx layer exceeds 6 meters, and the onyx lenses are spread in a very large desert surface (Ref: Photo 4 on page 2). 5.0 Processing: As is true of all sedimentary rock types, onyx is largely “anisotropic”, or directionally specific in both visual and strength properties. It can therefore be sawn in two distinctly different directions.One method, in which the slabs are sawn parallel to the layers of stratification, is known as a “fleuri” or “crosscut” direction. The other, in which case the slabs are sawn across the layers of stratification, is known as a “vein cut” or “veiny” direction (Ref: Figure 1 and Photos 5 through 8 in Photo Appendix). Since onyx is generally used as an interior, decorative stone, strength properties rarely govern the decision of which sawing direction shall be used. It is more common that the direction is determined by the specifier’s preference, or the general market demand.

In the current marketplace, the crosscut direction is more common, as it generally exploits the translucent feature of onyx more vividly than the vein cut direction. Vein cut slabs Are typically used when slab matching techniques such as “book matched” or “diamond matched” are employed (Ref: Appendix A). In some cases, vein cut slabs are not obtainable or practical due to the limited bed height of the quarry, which limits the block dimension in this direction. Onyx blocks are usually sawn to slab thickness using gangsaws of the same type with the same abrasive media as is used to saw marble blocks. While onyx can be sawn to any thickness, 20 mm slab thickness is overwhelmingly the most common. Due to limited stability of many onyx varieties, the block is typically reinforced prior to the sawing of the slabs. This treatment is for the prevention of slab breakage both during and after the sawing process. The block is covered with either plastic film or wood planks, but in either case the technique involves injecting epoxy resin which penetrates between the block and the covering material. A vacuum system is used to further draw the Resin into the interior regions of the stone fabric.

After the sawing operation, further processing of the slabs is necessary. In nearly all cases, the rear face of each slab is reinforced with a fiberglass mesh adhered with an epoxy, or possibly polyester based resin. This is both for stabilization of the slab and safety in the handling of the slab. On the primary face of the slab, a resin, typically epoxy, is screeded onto the slab surface. In the more sophisticated and automated production environments, the slab will be positioned over a vacuum source on the rear side, thus drawing the resin more deeply into any pores or fissures within the stone slab. Although the production is mechanized, the experience level of the operators calibrating and preparing the slabs is still very important, as the natural features of onyx slabs are widely variable, and each slab must be evaluated as a unique entity. The treatment of the slabs during this phase is extremely influential in the overall performance and/or appearance of the material. (Ref: Photo 10 in Photo Appendix) Once prepared as above, the slabs are ready to receive their face finish, which in most cases is a Polished finish.

The processing lines that are used to polish onyx are usually the same as those used to polish marbles and other stone types, although there have been some lines specifically engineered and built to polish onyx exclusively. The emphasis in polishing onyx slabs is not placed on production rates, but rather the quality of the polish. The goal is to achieve a polished surface of the highest and most uniform gloss, while preserving a nearly perfectly flat plane to provide mirror-like reflective properties. Modern factory finishes utilizing resin impregnation and polishing rarely require retouching by hand. Pressure applied by the polishing wheels, feed rates of the slabs, and the abrasive differ greatly from what is used on other rock types (limestone, granite and travertine), and will even vary significantly between different varieties of onyx. 6.0 Practical Considerations when working with Onyx and Onyx-like Materials: The Marble Institute of America’s soundness classification for marbles is well known in the industry. In this system, soundness classifications “C” and “D” are not recommended for exterior or wet area installation.

A number of onyxes have been classified by this same system, and they are all classified as soundness “C” or “D” stones, which makes them inappropriate choices for exterior application. The weathering characteristics of onyx are quite poor, to the extent that it is not recommended to store onyx slabs outdoors, even for short periods of time. Being products of nature, variability is to be expected when using any natural stone. Simply stated, no two slabs of onyx are the same. This fact, coupled with the typical usage of onyx as a decorative feature finish material, makes the selection and approval process particularly demanding. Onyx typically needs to be viewed in full sized slabs, and must be the actual slabs intended for use in the project. In many cases, the portion of the slab to be used, as well as the directional orientation must be clarified to ensure all parties have a thorough understanding of the intended stock utilization. Despite its vulnerability to moisture exposure, onyx is sometimes specified as a shower lining material, both in tile and slab application. Contact area of the adhesive is critical, and the material’s reaction to the water and steam might be deemed undesirable by some.

Oftentimes a seam or other separation plane within the stone fabric will “swell” over time, causing a “lifting” of the surface, to the extent that the occupants can feel the raised lip within the stone surface. This is simply a property of the material, and not considered a defect. Onyx is occasionally used in curtainwall applications as an accent or feature in interior or other weather protected areas. In this case, the onyx is generally polished on both surfaces, as the translucency of the product is exploited for visual effect. In some cases the onyx can be successfully captured by the the curtainwall system with 4- edge perimeter capture of a minimum ¾” (20 mm) embedment into the curtainwall frame. Larger panel sizes, reduced thicknesses (especially thicknesses less than 20 mm), or lower strength onyx may require that the stone be laminated to a glass panel for structural support. Lamination of onyx to glass or transparent plastic backers is a highly specialized area, and is done when the onyx is to be backlit to show the striking effect of the light passing through the translucent stone. Lamination may also be required to achieve code compliance for public safety reasons.

Flexural strength of onyx is low when compared to many other stone varieties, and is frequently in the 500 to 750 lbs/in² (3.4 to 5.2 Mpa) range. This property, coupled with a brittle breaking behavior, makes bonding area critical. Compliance with the MIA guidelines of coverage and void restrictions is imperative. Additionally, substrate rigidity is critical, and MIA substrate deflection limits must be observed. Many varieties of onyx have reduced stain resistance, and measures should be taken to prevent staining from related construction products. White portland cement based thinset adhesives are recommended, and tests should be performed with the actual adhesive and actual onyx to ascertain compatibility. These tests should be run for a minimum of two weeks to allow for substantial cure of the thinset. Grout dyes are probably best avoided altogether, but if used, must be thoroughly tested to assess staining potential. Many joint sealants have oil-based plasticizers included in their formulation, and these have been known to migrate into stone edges and cause staining. Stain testing of sealants should be performed per ASTM C1248.

When designing an anchored system with onyx, it should be noted that anchors (such as strap anchors) requiring a kerf preparation in the stone edge are of extremely low capacity in thin (.., .20 mm) slab onyx material. Anchors that require very small holes (.1/8h, .3 mm diameter) such as stainless steel pins or wire anchors will generally perform better. Substrate and frame systems that allow the field mechanic to drill these holes on site and allow some latitude in the anchor placement are advantageous, as the field mechanic can then avoid positioning of the anchor coincident with a natural seam or other separation plane in the stone panel. Due to the translucency of onyx, light will be transmitted through it even if not in a backlit application. The path of at least some of this light energy will be nearly parallel to the face of the stone. When an opaque joint filler is used, the opacity of the filler blocks the light transmission at that point. This can cause a dark shadow to appear along the perimeter of the onyx panels, even though there is no color difference in the material, only an interruption in the path of the light.

Onyx makes a beautiful flooring surface, but its low level of abrasion resistance generally limits flooring application to residential applications. Even in these light duty exposures, if a polished onyx is used, a reduction in surface gloss should be anticipated as a result of the foot traffic abrasion. It is advisable for the stone professional to Exercise caution when onyx is specified for commercial applications. Selecting onyx for a commercial application must be reviewed in the design phase, and expectations of traffic pattern wear and breakage due to every day use must be understood to all parties involved in the project. Onyx is frequently used for bar tops, but surface degradation to the onyx should be anticipated. Mild acids can etch the surface, and the sliding of service items across the surface can abrade the stone. Honed surfaces are less likely to manifest the etches and scratches, since they won’t exhibit the gloss variation as does a polished surface. One of the primary vulnerabilities of onyx is its susceptibility to chipping during fabrication. Since all onyxes are unique, some experimentation will be required, but as a general rule, cutting with continuous rim diamond blades designed for marble and polishing using pads designed for marble is likely to be the most successful.

Ironically, what makes onyx beautiful is also what makes it challenging to work. As a heterogeneous material of sedimentary origin, natural onyx is typically going to have numerous “seams”, “starts”, “voids”, and mineral discontinuities that require either repair or reinforcement before the material can be used. Whether performed in the shop or field setting, these repairs are both necessary and permissible, as outlined by the MIA’s Soundness Classification system (Ref: Marble Institute of America Technical Bulletin on Marble Soundness, 2005). Customer Education is paramount when supplying onyx products. The types and extents of repair and reinforcement, the vulnerabilities of the product, and the “patina”, or anticipated changes in appearance over the service life of the application must be thoroughly discussed with the customer during the initial phases of the selection process. 7.0 Onyx Properties and Specifications: Within ASTM, all Specifications, Guides, and Test Methods for dimension stone are under the jurisdiction of Committee C18. This committee has drafted specifications listing the expected values for physical and mechanical property values for most species of dimension stone.

For instance, limestone is governed by ASTM C568, Specification for Limestone Dimension Stone, and granite is governed by ASTM C615, Specification for Granite Dimension Stone. The work of this committee has traditionally focused more on stones used in exterior application, and has only recently begun publishing documents pertaining to interior stone applications. Because of this, there has never been an ASTM specification published governing physical and mechanical properties of onyx. So while the same test methods can be used to determine the values, there is no specification to which those values can be compared for evaluation. Many have used the marble specification, C503, as benchmark values, but this is not an endorsed practice, since marble and onyx differ greatly in structure and performance. Typical property values of onyxes on the market are listed in the table on the next page. 8.0 Summary: This highly decorative stone variety is appreciated by all, but none will appreciate it at the level of one who has actually worked “hands-on” with this challenging, yet rewarding creation of nature. Many of the processes involved in successfully completing a detailed onyx application can be executed only at the hands of a true artisan of the trade.

While mechanization and computerization of many processes have made the working of onyx more efficient, these materials will never fully surrender their requirement to be recognized and treated as unique individuals. Therein lies the true beauty of onyx. Sources: 2. Dimension Stone in ACP Countries, 3. Lombardy Stone Association, 4. Marble Institute of America, and 5. Royal Debid Stone Thank You: The MIA extends special thanks to Marco Farsetti, Quema S.r.l., Italy, for his original draft, guidance and consultation producing this technical bulletin. We also would like to acknowledge the contributions of Jonathan Zanger, Walker Zanger, Inc.; Brett Rugo, Rugo Stone LLC; John McDowell, Rocky Mountain Stone Co., Inc.; Ali R. Tehrani, Primestone, Canada; and W.A. Bothner, Professor Emeritus of Geology, University of New Hampshire, Durham, NH.

Appendix B: Glossary of Terms Alabaster: A fibrous variety of gypsum (porous) Anhydrite: CaS04 (essentially gypsum without the water of crystallization) Aragonite: CaC03 (same composition as calcite, but a different crystal structure) Calcite: CaC03 (primary mineral of limestone and marble) Chalcedony: A cryptocrystalline variety of quartz…may be translucent or semitransparent and nearly a wax-like luster…varieties include onyx and sardonyx. Gypsum: CaS04•2H20 (the water is part of the crystal structure) Onyx: Variety of chalcedony that is like banded agate…alternating bands of different colors which are roughly parallel. The name onyx is used on two different rock types: siliceous onyx and calcareous onyx. In the mineralogical literature the term onyx indicates a (black and white) banded siliceous rock composed of chalcedony, a crypto crystalline variety of quartz.

However, in recent time, the term onyx has been used in the commercial field for calcareous banded material. This is sometimes referred to as onyx marble or marble onyx. Onyx Marble: Also “Marble Onyx”; Compact, usually banded, generally translucent variety of calcite resembling true onyx. Generally deposited from cold water solution. Siliceous Sinter: Lightweight porous opaline variety of silica. Precipitated from waters of geysers and hot springs. Example, Mammoth Hot Springs in Yellowstone. Read the full article at .

Question: What name, derived from the Greek word for chalk, is given to hydrated calcium sulphate?
Answer: GYPSUM